In the manufacture of laminated panes, notably safety panes formed of two glass sheets and an intermediate sheet or layer of plastics material (for example, a polyvinylbutyral or polyurethane), the elements forming each pane are assembled together by stacking of the elements. The stacking step is generally followed by calendering by passage of the stack between press rollers and an autoclave cycle.
At the time of stacking the elements, the intermediate sheet of plastics material is in the form of a blank which is generally quadralateral. The dimensions of the quadralateral blank are slightly greater than those of the pane to be produced.
After stacking and before calendering, the parts of the intermediate sheet which extend beyond the glass sheets are cut manually by trimming the edge using a metal blade, the operator who carries out this cutting holding the blade in contact against the edge of the glass sheets. This is a manual operation which is long and expensive. Also, the manual operation is frequently found to have been imprecise, and it is then necessary to carry out further trimming (generally after the autoclave cycle) in order to remove the parts of the intermediate plastic sheet which still extend beyond the glass sheet.
Another disadvantage of the manual cutting operation is that the tool runs the risk of attacking the edges of the glass sheets and thus of making the pane fragile.
Further, the width of the material removed cannot generally be less than a certain value.
Manual operations also risk causing soiling or fall of unwanted material into the internal parts of the stack, thus causing rejects or inferior quality.
Finally, the blades used for the manual operation wear out very rapidly and have to be changed frequently.
Automatic cutting devices have already been described (for example, in French patent publication No. 2,510,029 and in British patent publication No. 2,144,363). However, these devices are not entirely satisfactory.
One of the problems encountered in automatic cutting is control of the temperature of the cutting tool. It has been found that, to obtain a clean and correct cut on the one hand and to improve the life of the tool on the other hand, the cutting tool should have a temperature which is at least approximately constant during the whole cutting operation. The automatic devices disclosed in the patent publication mentioned above do not provide adequate temperature regulation.
Another problem encountered in automatic cutting is that of the flexibility of the sheet of plastics material. This lack of rigidity causes sinking of the parts of the intermediate sheet which extend beyond the glass sheets and a poor supporting of the parts of the intermediate plastic sheet facing the cutting tool.